The prior art packaging of printed circuit boards containing electronic circuitry to prevent EMI signals from leaving the package or from reaching and adversely affecting highly-susceptible electronic circuitry within the package is both labor intensive to manufacture and service and suffers from several functional limitations. Keeping EMI from leaving an electronics module that contains EMI-emitting components has required soldering certain shielding materials to the printed circuit board and fastening other shielding materials to the soldered shielding material using various screws or other fastening hardware. Keeping EMI from reaching and affecting susceptible electronic circuits in an electronics module, on the other hand, has required placing the printed circuit board fully in a sealed box made of a material that the effectively shields most of the EMI signals.
In typical packages that shield EMI emitting components, several pieces are soldered to the printed circuit board and as many as 20 or more pieces of fastening hardware affix to the soldered pieces to provide the necessary level of shielding. This labor-intensive practice of soldering and fastening prior art shielding enclosures to printed circuit boards increases the electronics module fabrication costs. Moreover, with prior art shielding enclosures it is not possible to easily replace or repair electronic circuitry components on the printed circuit board. This is due to circuitry components often being tightly positioned adjacent the soldered shield pieces that are not easily removable from the printed circuit board. This causes servicing EMI-shielded printed circuit boards also to be time-consuming and expensive.
Prior art packaging for preventing EMI signals from reaching and affecting EMI susceptible circuits in an electronics module suffers from other limitations. Using soldered and fastened shield materials is generally impractical because an unacceptable level of EMI leakage often occurs in such designs. Therefore, prior art devices for shielding susceptible electronic circuits from EMI use sealed boxes made of aluminum or some other electrically conductive material that fully enclose the printed circuit board. The EMI shield boxes of the prior art have sealed edges that keep EMI away from the sensitive electronic circuitry while often providing a way for radio frequency signals to reach the electronic circuits. These types of sealed EMI shield boxes, however, are cumbersome, expensive, labor intensive and require significant amounts of storage space in electronics cabinets designed to hold them.
An even more serious limitation that the prior art EMI shield boxes impose relates to the fact that numerous electronics cabinet designs call for easy installation and removal of the shielded electronics module. Some newer electronics cabinet designs require that the printed circuit boards be directly plugged into the electronics cabinets. This requires exposing a large portion of the printed circuit board outside the EMI shield. With the prior art EMI shield boxes, however, exposing the printed circuit board makes it possible for EMI to pass through the printed circuit board and to the susceptible electronic circuitry.
It is thus an object of the present invention to provide a shielding apparatus for electronic circuitry on a printed circuit board that allows solderless installation of an EMI shield to produce an electronics module that has a high degree of EMI shielding and that permits extensive communication of desired electromagnetic radio frequency and electrical signals by exposing from out of the EMI shield certain portions of the printed circuit board.